cfg_if::cfg_if! {
    if #[cfg(feature = "postgres")] {
        pub fn foo() {
            postgres();
        }
    } else if #[cfg(feature = "mysql")] {
       pub fn foo() {
            mysql();
        }
    } else {
        pub fn foo() {
            println!("no feature");
        }
    }
}

#[cfg(feature = "postgres")]
fn postgres() {
    println!("postgres")
}

#[cfg(feature = "mysql")]
fn mysql() {
    println!("mysql")
}
